ath9k_htc: Fix error path in URB allocation

ath9k_hif_usb_alloc_urbs() takes care of freeing
all the allocated URBs for the various endpoints when
an error occurs. Calling ath9k_hif_usb_dealloc_urbs() would
cause a panic since the URBs have already been freed.

Signed-off-by: Sujith Manoharan <Sujith.Manoharan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>